In some countries with relatively harsh, long winters, such as for example some parts of some Scandinavian countries, studded winter tires are used relatively extensively to enhance tire tread traction on icy roads. However, the use of studded tires, namely tire treads containing metallic studs, have sometimes been somewhat restricted at least in part due to potential damage to roads.
For many years, non-studded winter tires have been used which have tread rubber compositions composed of elastomers which have low glass transition temperatures (Tg's), namely Tg's below -30.degree. C. Such low Tg elastomers are typically used to inhibit or at least reduce excessive hardening of the tread rubber composition at the very low ambient operating temperatures.
Also, silica reinforcement of selected elastomers have been used for tire treads intended for winter conditions. For example, see U.S. Pat. No. 5,616,639.
Other winter tread rubber compositions designed to improve tire traction on ice include the aforesaid use of low Tg rubbers, as well as use of low temperature plasticizers designed to provide a general reduction of the tread composition's hardness at low temperatures.
However, it is considered herein that it is still desired to provide tire treads with enhanced traction on roads which are icy for extended periods of time.
Historically, substantial amounts of silica reinforcement in combination with a silica coupling agent has sometimes been used as a primary or predominant reinforcement for various rubber blends in rubber tire treads. For example, see U.S. Pat. Nos. 4,519,430; 5,066,721; 5,227,425 and 5,616,639. Use of various coupling agents to achieve reinforcement of the rubber composition by coupling the silica to the elastomer(s) is well known. However, it is considered herein that such silica/coupler reinforcement is often not, by itself, entirely sufficient for suitably enhanced ice traction for a tire tread.
While it is understood that cellulose fibers have been previously suggested for use in earthmover tire treads to reduce cut propagation in the tire tread rubber composition and that resorcinol/formaldehyde type bonding systems have sometimes been used to bond such fibers to the resin network of the tread rubber composition compounds, it is considered herein that the subject of ice traction for such tread compositions has not been addressed.
In the description of this invention, the terms "rubber" and "elastomer" where used herein unless otherwise prescribed, are used interchangeably. The terms rubber "composition" or "compound" where used herein, unless otherwise prescribed, generally refers to a composition in which one or several rubbers are blended or mixed with various ingredients or materials. A term "compounding ingredient" where used herein unless otherwise prescribed, generally refers to ingredients used to prepare rubber compositions, or compounds. Such terms are well known to those having skill in the rubber mixing and compounding art.
The term "phr", where used herein and according to conventional practice, refers to parts by weight of respective material per 100 parts by weight of rubber.
The Tg of a rubber or rubber compound, as used herein unless otherwise prescribed, refers to its glass transition temperature which can be conventionally be determined, for example, by differential scanning calorimetrie at a heating rate of 10.degree. C. per minute. It is understood that such Tg determination is well known to those having skill in such art.